• Journal of Positioning, Navigation, and Timing
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• v.13 no.2
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• pp.189-197
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• 2024

Galileo is a European Global Navigation Satellite System (GNSS) that has offered the Galileo Open Service since 2016. Consequently, the standardization of GNSS augmentation systems, such as Satellite Based Augmentation System (SBAS), Ground Based Augmentation System (GBAS), and Aircraft Based Augmentation System (ABAS) for Galileo signals, is ongoing. In 2023, the European Union Space Programme Agency (EUSPA) released prior probabilities of a satellite fault and a constellation fault for Galileo, which are 3×10^-5 and 2×10^-4 per hour, respectively. In particular, the prior probability of a Galileo constellation fault is significantly higher than that for the GPS constellation fault, which is defined as 1×10^-8 per hour. This raised concerns about its potential impact on GBAS integrity monitoring. According to the Global Positioning System (GPS) Standard Positioning Service Performance Standard (SPS PS), a constellation fault is classified as a wide fault. A wide fault refers to a fault that affects more than two satellites due to a common cause. Such a fault can be caused by a failure in the Earth Orientation Parameter (EOP). The EOP is used when transforming the inertial axis, on which the orbit determination is based, to Earth Centered Earth Fixed (ECEF) axis, accounting for the irregularities in the rotation of the Earth. Therefore, a faulty EOP can introduce errors when computing a satellite position with respect to the ECEF axis. In GNSS, the ephemeris parameters are estimated based on the positions of satellites and are transmitted to navigation satellites. Subsequently, these ephemeris parameters are broadcasted via the navigation message to users. Therefore, a faulty EOP results in erroneous broadcast ephemeris data. In this paper, we assess the conventional ephemeris fault detection monitor currently employed in GBAS for wide faults, as current GBAS considers only single failure cases. In addition to the existing requirements defined in the standards on the Probability of Missed Detection (PMD), we derive a new PMD requirement tailored for a wide fault. The compliance of the current ephemeris monitor to the derived requirement is evaluated through a simulation. Our findings confirm that the conventional monitor meets the requirement even for wide fault scenarios.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.6
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• pp.453-460
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• 2014

We analyze fault detection algorithm of ephemeris included in navigation message, which is one of the GNSS risk factors. This algorithm uses carrier-phase measurement and baseline vector of two reference stations and is alternative method for uncertainty condition of previous ephemeris. Even though same ephemeris fault is occurred, the geometry condition, between baseline vector of reference stations and satellites, effects on performance of algorithm. Also, we introduce the suitable geometry of reference stations, threshold and performance index (MDE : Minimum Detectable Error) in jeju international airport.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.263-269
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• 2021

The carrier-based differential global navigation satellite system (CD-GNSS) has been garnering significant attention as a promising technology for unmanned vehicles for its high accuracy. The CD-GNSS systems to be used for safety-critical applications should provide a certain level of integrity. The integrity of these systems must be analyzed under various conditions, including fault-free and satellite fault conditions. The systems should be able to detect the faults that can cause large biases on the user position errors and quantify the integrity risk by computing the protection level (PL) to protect the user against the faults that are left undetected. Prior work has derived and investigated the PL for the fault-free condition. In this study, the integrity of the CD-GNSS system under the fault condition is analyzed. The position errors caused by the satellite's fault are compared with the fault-free PL (PL_H0) to verify whether the integrity requirement can be met without computing the PLs for the fault conditions. The simulations are conducted by assuming the ephemeris fault, and the position errors are evaluated by changing the size of the ephemeris faults that missed detection. It was confirmed that the existing fault monitors do not guarantee that the position error under the fault condition does not exceed the PL_H0. Further, the impact of the faults on the position errors is discussed.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.89-101
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• 2015

To satisfy civil aviation requirements using the Global Navigation Satellite System (GNSS), it is important to guarantee system integrity. In this work, we propose a fault detection algorithm for GNSS ephemeris anomalies. The basic principle concerns baseline length estimation with GNSS measurements (pseudorange, broadcasted ephemerides). The estimated baseline length is subtracted from the true baseline length, computed using the exact surveyed ground antenna positions. If this subtracted value differs by more than a given threshold, this indicates that an ephemeris anomaly has been detected. This algorithm is suitable for detecting Type A ephemeris failure, and more advantageous for use with multiple stations with various long baseline vectors. The principles of the algorithm, sensitivity analysis, minimum detectable error (MDE), and protection level derivation are described and we verify the sensitivity analysis and algorithm availability based on real GPS data in Korea. Consequently, this algorithm is appropriate for GNSS regional implementation.

• Journal of Advanced Navigation Technology
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• v.14 no.5
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• pp.610-617
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• 2010

This paper analyzes the characteristics of abnormal broadcast GPS ephemeris by comparing distances between the receiver and the satellites. Effects of abnormal ephemeris on receiver's position estimate are closely related with range errors caused by variations of satellite positions. In more detail each range error depends on the satellite position error and the line of sight vector. Based on the fact, the ephemeris parameters are classified into three types depending on the size, the shape, and the shape of the satellite orbit to analyze the fault characteristics. The effects of satellite position errors caused by the three type s of parameters on the receiver's position estimate are analyze d in detail.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.27-36
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• 2014

Generally, satellites continuously monitor that its major functions are working properly and their hardware are in a good status using several SOH data. In case a fault that is not recognized as a temporal problem or a failure that can be considered to propagate its damage to the other parts are detected, fault management logic is performed automatically without any contact of ground station. In this paper, attitude error detection using sun sensors on a rotating solar array is proposed. Attitude error can be detected by comparing the offset angle between the actual data computed from the sun sensor and the data predicted from the orbit and ephemeris information for the two types of solar array operation method. During the eclipse, the output of attitude error detection method becomes zero because the sun sensor output cannot be provided. Finally, the proposed method is analyzed through the data processing using on-orbit data.